The present invention relates to hydraulic systems, and in particular to hydraulic systems used on refuse collection vehicles to compact refuse and operate auxiliary hydraulic equipment such as refuse cart lifting devices.
Refuse collection vehicle hydraulic systems are primarily used to operate a ram that drives a packer panel, which compacts refuse dumped into the refuse collection vehicle's hopper. Many refuse collection vehicles are often also equipped with hydraulically operated auxiliary equipment such as refuse cart lifters. Refuse cart lifters are commonly known as lifters or tippers because they assist the vehicle operator in lifting and tipping heavy refuse carts into the refuse collection vehicle hopper or intermediate container.
A flow diverting apparatus, is commonly used to divert hydraulic fluid flow out of the main hydraulic system into the lifter circuit that operates these refuse cart lifting devices. The use of a flow-diverting apparatus, such as a diverter control assembly, to control hydraulic fluid flow to auxiliary hydraulic circuits is well known to those familiar with the design and operation of hydraulic systems.
Flow can be diverted by numerous means. The simplest method involves nothing more than a tee fitting placed in line of one of the pressure lines, with the primary flow directed towards the packer panel ram and the tee flow being directed to the lifter circuit. There are, however, several problems associated with this type of simple system. For example, the simple tee system will not maintain a consistent flow to the refuse cart lifters. The flow to the refuse cart lifters will be proportional to the flow to the downstream functions (such as the refuse collection vehicle packer ram) based on the size of the hydraulic lines and the downstream back pressure.
As inlet flow increases, the outlet flows increase and remain proportional to each other. This is because mobile refuse collection equipment typically utilizes a positive displacement “power take off” pump to provide refuse collection vehicle hydraulic system flow and pressure. The amount of hydraulic fluid flow in the system varies with the speed of the pump, and the pump speed directly corresponds to the refuse collection vehicle engine speed. Thus, the simple tee system cannot control the amount of hydraulic fluid flow to the refuse cart lifters as pump speeds vary.
Hydraulic refuse cart lifters require more precise control of hydraulic fluid flow. The time of the refuse cart lifter operating cycle is critical to performance, life of the refuse cart lifter, and life of the refuse cart. Most refuse cart lifters require a flow of 2 to 2.5 gallons per minute (gpm). The simple tee system can be improved by placing an orifice in the outlet line to the refuse cart lifters. This will change the proportion of flow and restrict the flow to a more suitable level.
For example, diverter control assemblies may use a priority flow valve containing an orifice. However, the pressure required to operate the priority flow valve is high, causing a pressure drop across the block. In order to maintain a controlled flow to two refuse cart lifters, a flow divider valve may be used to evenly divide the flow provided by the priority flow valve. However, when the refuse cart lifter bottoms out or the flow divider valve fails, the priority flow valve will shut down flow to downstream functions.
Moreover, this configuration can require significantly more pressure to operate than the priority flow valve. In fact, the pressure drop is more than doubled in the dual refuse cart lifter configuration. The combination of the two devices causes the pressure drop in the valve to be very high (as high as 350 to 400 psi, or more in certain instances). However, all mobile refuse equipment is not the same. System flow rates can range from less than 20 gpm to more than 60 gpm. The simple tee system is therefore often equipped with an adjustable orifice so that the flow can be fine tuned to make the flow to the refuse cart lifters acceptable regardless of the flow coming in to the tee. This relatively inexpensive type of flow diverter technology is currently used in many systems, but presents many disadvantages when used to control flow to refuse cart lifters.
For example, once the flow to the refuse cart lifters is adjusted, it will still allow for the flow to vary with the primary system flow. This will cause the refuse cart lifters to operate at different speeds relative to the primary system flow. Moreover, the use of a variable orifice results in a significant pressure drop across the system. This causes a reduction in the pressure available to downstream operations and can noticeably affect their operation and performance.
Furthermore, the additional work being done to move the oil through this restriction is dissipated through heat. The addition of heat to the hydraulic system is generally unacceptable as it also reduces the performance of the system. It can also be dangerous and lead to potential component failures and possibly system fires. Finally, if the adjustable orifice is improperly adjusted, it may allow the refuse cart lifters to cycle too quickly and lead to premature lifter failure and cart damage, or even personal injury.